Friday, May 3, 2013
Magnetic Resonance Imaging for Measurement of Velocity and Concentration in Complex Turbulent Flows
John Eaton, Professor, Center for Turbulence Research, Mechanical Engineering, Stanford University
Magnetic Resonance Imaging (MRI) based flow measurement techniques are enabling a paradigm shift in how we study, evaluate, and design turbulent flows in complex geometries. MR Velocimetry (MRV) measures a complete 3-D mean velocity field and does not require flow tracers or optical access. Resolutions as fine as 0.25 mm have been achieved in measurement volumes as large as 100 mm X 100 mm X 250 mm. An entire velocity field comprising millions of individual data points can be measured in a few hours. Example applications include the flow around a coral colony, internal flows in serpentine passages, separated flows in three dimensional diffusers, and turbine film cooling systems. The detailed 3D measurements allow understanding of vortex structures which dominate many flows, the interplay between separation zones, and analysis of flow splits among parallel paths. A second technique called Magnetic Resonance Concentration (MRC) provides quantitative measurements of the time-averaged 3D concentration field for passive scalar mixing. The combination of measured 3D concentration and velocity fields provides enough detail to yield exceptional understanding of the effects of mean flow transport and turbulent mixing. This has proved particularly effective in the iterative design of film-cooling and diffuser systems where we wish to either suppress or enhance mixing. In addition, the combined velocity and concentration data are being used to optimize Reynolds-averaged models for turbulent mixing.